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New Pig Virus Renews Transplant Concerns

Pigs harbor two kinds of viruses that can infect human cells in the laboratory, researchers report in today's issue of Nature. The discovery is a further blow to hopes that pig organs might relieve the chronic shortage of donor organs for transplantation into people.

A major worry about the safety of transplanting animal organs into people is that animal viruses might jump the species barrier and infect immune-suppressed patients. Earlier this year, a British research team discovered retroviruses called porcine endogenous proviruses (PERVs) in lab cultures of pig cells and showed that they could infect human cells (ScienceNOW, 27 February).

Jonathan Stoye and Paul Tissier at the National Institute for Medical Research, and colleagues at the Institute for Cancer Research in London, set out to study the PERVs' surface coat from PERVs in lab cultures of pig and infected human cells to look for clues as to which viruses can enter human cells. To their surprise, they found two types of retrovirus--called PERV-A and PERV-B--in normal tissues in a number of different pig breeds. The viruses were present in all tissues tested, including heart and kidney, and both could infect cultured human cells.

The researchers now think the prevalence of these retroviruses could make it hard to purge them from potential donor breeds of pigs. "We may have to go ahead with clinical transplant trials of organs from virus-infected animals," says Stoye. "But it will be very important to monitor these viruses very carefully." The viruses appear to cause the pigs no harm, and it is unclear whether the viruses could cause human illness.

At least one biotech company is not ruffled by the finding. "We were already aware of at least three variants of porcine retroviruses," says a spokesperson for Imutran, a British company developing pigs with a genetically altered immune system to prevent rejection of transplanted organs in people. But, she adds, "we need to know whether they can infect normal human cells and, if so, whether they would cause a problem."